Field of the Invention
The present invention relates to a composition for forming a resist underlayer film that is effective as an antireflective film material used for fine patterning in a manufacturing process of a semiconductor device, etc., and to a resist patterning process using the same that is suitable for exposure by far ultraviolet rays, KrF excimer laser beam (248 nm), ArF excimer laser beam (193 nm), F2 laser beam (157 nm), Kr2 laser beam (146 nm), Ar2 laser beam (126 nm), soft X-rays (EUV, 13.5 nm), electron beam (EB), X-rays or the like.
Description of the Related Art
A finer pattern rule has been recently required for Large-Scale Integrated circuit (LSI) with higher integration and higher processing speed. Under such circumstances, lithography using photo-exposure, which has been currently used as a general technique, develops to achieve a finer and more precise pattern processing according to a light source used therein.
As the light source for lithography employed in resist patterning, g-beam (436 nm) or i-beam (365 nm) of mercury lamp has been widely used in the photo-exposure. Shifting the exposure light to shorter wavelength was assumed to be effective in finer patterning. Thus, KrF excimer laser (248 nm), whose wavelength is shorter than i-beam (365 nm), has been used in place of i-beam as the exposure light source in mass production process of Dynamic Random Access Memory (DRAM) with 64 MB. However, production of DRAM with integration of 1 GB or higher, which requires still finer processing technologies (work size of 0.13 μm or less), needs a light source with still shorter wavelength, and lithography especially using ArF excimer laser (193 nm) is thus under investigation.
It is well known that a monolayer resist method, which is used as a typical resist patterning process, may cause pattern collapse at development due to surface tension of a developer if the ratio of pattern height to pattern line width (aspect ratio) is too high. To form a pattern with high aspect ratio on an uneven substrate, a multilayer resist method, in which films having different dry etching properties are laminated for patterning, is suitable. Then, there have been developed a two-layer resist process combining a resist layer of a photosensitive silicon polymer and an underlayer of an organic polymer mainly composed of carbon, hydrogen, and oxygen, for example, a novolak polymer (Patent Document 1); and a three-layer resist process combining a resist layer of a photosensitive organic polymer used in the monolayer resist method, a middle layer of a silicon polymer or a silicon CVD film, and an underlayer of an organic polymer (Patent Document 2).
In the multilayer resist method, the underlayer film uses the organic polymer mainly composed of carbon, hydrogen, and oxygen to form a pattern by dry etching with an oxygen gas by using the silicon-containing material film formed thereon as a hard mask. In addition to this, the underlayer film is required to have an etching resistance for dry etching of a substrate to be processed, an ability to form a film with high flatness on the substrate to be processed, and an antireflective function during photo-exposure depending on usage. For example, Patent Document 2, which relates to an underlayer film composition for two-layer or three-layer resist process, discloses that such an underlayer film enables formation of an underlayer film pattern with high precision and high etching resistance to etching conditions of the substrate to be processed.
FIG. 2 shows substrate reflectance when k-value (extinction coefficient) of the resist middle layer film is changed.
The appropriate film thickness in which the k-value of the resist middle layer film is 0.2 or lower yields a sufficient antireflective effect of 1% or less.
FIG. 3 and FIG. 4 show change of reflectance with change of film thicknesses of the middle layer film and the underlayer film in the case that the k-value of the underlayer film is 0.2 or 0.6, respectively. The resist underlayer film having higher k-value (in the case of 0.6 (FIG. 4)) can reduce the reflectance to 1% or less with the film being thinner. In the case that the k-value of the resist underlayer film is 0.2 (FIG. 3), the resist middle layer film 250 nm thick needs to be thicker to achieve a reflectance of 1%. However, it is undesirable to make the resist middle layer film thicker because the thicker film leads a larger load to the uppermost resist film at the time of dry etching for processing the resist middle layer film. FIG. 3 and FIG. 4, which show reflectance in the dry exposure by an exposure apparatus having lens with a numerical aperture (NA) of 0.85, indicate that reflectance of 1% or less can be achieved by optimizing the n-value (refractive index), k-value, and film thickness of the middle layer film in the three-layer process, regardless of the k-value of the underlayer film.
On the contrary, NA of the projection lens exceeds 1.0 by liquid immersion lithography, and an angle of incident light to the resist and the antireflective film under the resist becomes shallow accordingly. The antireflective film suppresses reflection not only by absorption of the film itself but also by a negating action due to interference effect of the light. The oblique incident light makes the interference effect small and thus increases the reflectance.
Among the films in the three-layer process, the middle layer film has an antireflective effect by the interference action of the light. The underlayer film is too thick for the interference action, and thus has no antireflective effect by the negating action due to the interference effect. Reflection from the underlayer film surface needs to be suppressed, so that the k-value needs to be less than 0.6 and the n-value needs to be near the value of the middle layer film thereon. If the transparency is excessively high due to a smaller k-value, reflection from the substrate takes place. Thus, when NA of liquid immersion exposure is 1.3, the k-value is preferably in the range of about 0.25 to 0.48. Target n-values of the middle layer film and the underlayer film are both near 1.7, which is the n-value of the resist. In particular, the ratio of the n-value to the k-value is preferably n/k=1.50/0.30 to 0.35, approximately.
It is reported that a decrease of a processed line width causes phenomena such as wiggling and bending of the underlayer film at the time of etching the substrate to be processed by using the underlayer film as a mask (Non-Patent Document 1). It is commonly known that an amorphous carbon film formed by CVD (hereinafter, referred to as “CVD-C film”) can reduce the amount of hydrogen atoms therein extremely and thus prevent wiggling very effectively.
However, in the case that the underlayment substrate to be processed has difference in level, the difference needs to be planarized by the underlayer film. Planarizing the underlayer film can prevent variation in film thicknesses of the middle layer film and the photoresist formed thereon and increases a focus margin in lithography.
The CVD-C film using a raw material such as methane gas, ethane gas, and acetylene gas is difficult to fill the difference in level so as to be flat. On the other hand, the underlayer film formed by spin coating can advantageously fill the gaps of the substrate.
As mentioned above, the CVD-C film is poor in filling property for filling gaps. In addition, a CVD apparatus is difficult to be introduced due to its price and occupied footprint area in some cases. If the wiggling problem can be solved by using an underlayer film composition capable of forming a film by the spin coating method, the process and equipment can be simplified advantageously.
Therefore, it is desired to develop an underlayer film composition and a method for forming an underlayer film that has suitable n-value, k-value, and filling property as an antireflective film, and has excellent pattern-bend resistance without causing wiggling in etching.